The 21% pay gap in IT is larger than the 17% national average, and a survey of women in the industry found 53% of them either believe their pay is not comparable to their male colleagues, or do not know.
Intellect's Perceptions of Equal Pay survey questioned 330 women on pay. Of the group, 57% do not think their company has a transparent pay structure.
There was a slight increase in the number of companies carrying out equal pay audits. Eight per cent of respondents said their company had carried out an audit - this was double the figure in the last two years.
Gillian Arnold, technical manager at IBM and chair of Intellect's Women in IT group, said, "We still have a pay gap of 17% for full-time women [in all industries], and that gap is wider, at 21%, for women working in the IT Industry.
"Whilst many women still believe that they are paid less than their male colleagues, they are aware that their companies are starting to do something about it."