The Malleus Maleficarum, one of the two principal sources, along with Scripture, by King James I as the justification for his Daemonologie, first made the case for women as witches, using stereotypes rooted in gender, such as a woman's sexual nature and femininity as the "weaker sex." James' Daemonologie extended upon this with its assertion that female witches were dominant over male witches by a ratio of 20:1. By the time of James' accession to the English throne, the identification first raised in the Maleficarum had lodged itself in the public consciousness.
We see this in Reginald Scot's assertion, before James became king of Scotland and England, that those accused of witchcraft were frequently feeble, helpless old women. We can see this in the witch trials of the time, which in England predominantly focused on female "witches."
We see this in the literature of the day, particularly "Macbeth," and its depiction of witches as female crones. There is some speculation that "Macbeth" may have been penned for James I, with the presence of witchcraft a nod to the sovereign's belief that witchcraft was a real and viable threat.
Finally, we have the nature of the accusations of witchcraft. Frequently, these allegations were levelled against weaker members of society in the aftermath of conflict, or were crimes of a sexual nature, such as the "theft" of a man's penis.
The question of whether witch hunting was originally conceived as, overtly, a woman hunt, is an open one; regardless of its origins, however, we find the evidence to be sufficient that by the time of King James I, witch hunting was in fact woman hunting.