We have to rethink the business of the garden creator. No one actually claims that Semiramis made them. Ctesias (400 BC) places the garden description suggestively in the middle of his descriptive catalogue of her other building projects but does not name her, nor even say that "she" did whatever.
Further, Diodorus (c.50 BC) comments at the end of Ctesias' long section on Semiramis, that according to Athenaeus (fl c.200 BC, i.e. after Berossus), she was NOT the queen but merely a concubine loved by Ninus for her extraordinary beauty.
I've also found another source than Finkel that includes the interpolation that it was not Semiramis but a later Assyrian king who made them for a concubine (or queen? - lost it again - Rollins' compilation, I think), so perhaps he's somewhat rehabilitated.
Berossus (258-253 BC, writing to refute Achaemenid views & justify Greek interference) denies that Semiramis built anything at all, and apparently attributes them to Nebuchadnezzar. Josephus (est. c.67 AD) renders him that way and emphatically rejects the claims for Semiramis. But Eusebius (314 AD) tacitly rejects that part of his text, preferring an older tradition (Megasthenes, est c.310 BC) that sets Nebuchadnezzar's gardens in Teredon.
We do have hints, though, that Nebuchadnezzar had a wife named Nitocris - or possibly she was his daughter, or I think perhaps both. She may also have been the mother or wife or sister (or all three) of Belshazzar who saw the writing on the wall. Belshazzar was Nebuchadnezzar's son according to the Bible account, and he was the last of the Chaldeans/Neo-Babylonians. These were conquered by the Achaemenids, of whom Parysatis was one.
Nitocris has other possibilities. Herodotus says she was the fourth generation after Semiramis and a great builder. This Nitocris was Egyptian, and of course incredibly beautiful. And some sites suggest that she too has been accredited with the gardens. She is certainly as good a candidate as Semiramis or Nebuchadnezzar, who were also great builders. I think it also possible that the two Nitocrises have been conflated to produce the incredibly beautiful queen/concubine by/for whom the gardens were made, and this conflation could then be grafted onto Neb's gardens in Teredon, and thence to the existing gardens in Babylon.
Now, I still think Ctesias' history is fascinating. It certainly seems to be in conflict with others where these are itemized. But the fact remains that his description of the gardens is not only the earliest but the most coherent. So I think he was describing something real, and doing so fairly reliably. By extension, I therefore wonder if his reputation for unreliability is due to a misunderstanding by later historians.
Of course, his history focusses on women and eunuchs, and that alerts me to the possibility that it is a women's history, rather than a standard political history. Even so, we would expect the historical components that get into it to be accurate, and apparently they are not. (see a list here, from about note 23 ff) Reinhold Bichler regards this as "persiflage" (banter) - as if this was a sort of National Enquirer history that assumed the reader knew the reality and could thus enjoy the wit and humour of this madness.
It is also worth noting, though, that if you keep track of who these women were, what you find is that they seem to have a prorogative of protecting, promoting and avenging their male blood kin. That is fathers and brothers and possibly sons (but check this, in case they are mere incubators), but never husbands. By marrying their fathers and brothers, therefore, the women forge a much tighter alliance than they would if they married someone outside their family. And it seems they can force their husbands to help them exercise their prorogative of revenge.
The men also benefit from this arrangement, as they can be certain of their wife's loyalty when she is blood kin, because blood kin are the ONLY people the women can act for. The men, too, act for their blood relations, but not for plain wives. Thus Ataterxes grieved for Statira when his mother Parysatis killed her, but did not stay estranged from Parysatis. Parysatis killed Statira because Statira had avenged her brother against Parysatis.
Since Ctesias tells us that one of his main sources was Parysatis, I wonder if this was actually Parysatis' history, and that the misinformation and misrepresentations are hers, and that they serve as justifications or potential justifications for future actions. This seems borne out by Ctesias' apparent purpose in writing as suggested by Genest (linked below).
For Ctesias' & Berossus' purposes in writing (used here) see this site
If this is Parysatis' history, why would it suit her to imply that the gardens were made by Semiramis - and why did she not make the outright claim? I wonder if there was some proof when these histories were written about who actually did build the gardens? In any case, I would guess that it would NOT have suited her to credit them to Nebuchadnezzar, or to Nitocris the Egyptian, or Nitocris the Chaldean, since these were not her kin. In fact, Parysatis' Achaemenid kin conquered Nebuchadnezzar's Chaldean & Median kin, and Nebuchadnezzar's Chaldean/Median kin conquered Semiramis' Assyrian kin - and Semiramis had warred with the Medes. So the Chaldeans are out for Parysatis. Genest says that Ctesias noted that the Assyrian empire was the model the Achaemenids sought to follow.
Nebuchadnezzar's claim is made by Berossus - if the Irish analogy works, perhaps Berossus was keen to refute Achaemenid claims as well as ancient Assyrian claims (yes, he was, he wrote for the Greeks to justify their jurisdiction in Mesopotamia by rehabilitating the Chaldeans/Medes/Neo-Babylonians who had been conquered by the Achaemenid/Persians who also expanded over Greece, prior to Alexander I reconquering 331 BC - following turmoil after Alex's death in 323 BC, Babylon was evacuated to Greek-controlled Seleucia in 275 BC. Berossus wrote from there (I think) for Antiochus I). That would explain the diatribes against the Greeks and against Semiramis. The direct claim also seems important to me. If Berossus really did make that claim for the gardens, I think he probably could prove it in a legal sense at least - I'm thinking of the equally old Teredon gardens that might possibly be graftable onto Babylon (where there are no cuneiform records of the gardens).
According to some Bible study site, Nebuchadnezzar was married to Nitocris as well as to Amytis. Both these women are presented from time to time as having built or requested the gardens - so both are effectively part of the Nebuchadnezzar claim.
I think all this may matter because of the territorial rights that go with building. By analogy with Ireland, I suggest that building on someone else's land gives the builder rights of jurisdiction - so if the conquering Chaldeans built on Assyrian Babylon (which they did), that would have consolidated their rights. But if it could be argued that they merely rebuilt, perhaps that would reduce their rights. It is easy enough to make this claim for the walls and such, but the garden might have to be handled by implication alone.
So, given Ctesias' failure to make a solid claim, I think we can RULE OUT Semiramis. Nebuchadnezzar and/or his circle remains a possibility, however.
So we have three considerations for further investigation.
Semiramis is set up under the Achemaenids against the Chaldean/Medes; Nebuchadnezzar is set up under Alexander against the Achaemenid/Persians. But the Greeks didn't need this because Herodotus had already justified the Greeks by establishing that the Persians had no right to avenge Troy (one of their annexed Greek cities) because they were not an established empire at the time (Troy). Berossus is also rude about Greek writers - perhaps that also alienated his audience.
King list of Babylon
Semiramis - inc support for her as conc.
Assyrian Kings Samsi-Adad V ruled Assyria 823 BC
Piece on Babylon - cf section 27 for kujunjik relief, also other sections in gen. Several useful short articles on that site.