Women working for Facebook's UK division get nearly half the amount of bonus pay than their male counterparts, despite a similar proportion of each sex getting some kind of top-up award.
The median gender bonus pay gap at the business is 41.5%, according to figures submitted to the government.
However, the equivalent gap for hourly pay was much smaller - 9.9%.
That means when comparing median hourly rates, Facebook's female staff earn 90p for every £1 that its men earn.
That headline figure compares favourably to Google UK, which reported a 16% median hourly rate gender pay gap earlier this week.
Facebook employs about 1,500 people in the UK.
Its data states that 87.8% of its male workers got a bonus payment compared to 86.3% of its female employees.
It told the BBC that part of the reason there was such a big gap in the amount they received was because a higher proportion of its engineering teams and top-level executives were male than other areas of the business.
"Technical roles generally have a higher market rate than other positions due to their more specialised skills, but also the higher rate of demand for those skills in the marketplace," explained Fiona Mullan, the company's human resources chief for Europe, the Middle East and Africa.
"And the same would be true for leadership positions."
She added that the company hoped to tackle the discrepancy, but that would involve more females being encouraged to study relevant subjects at school and university.
"It really requires a back to basics approach, and will require more than the efforts of Facebook to change fundamentally the difference between the representation of men and women in the workplace particularly in technical careers," said Ms Mullan.
"This is a societal issue."
Organisations with more than 250 workers have until 4 April to publish their own pay gap data. The figures are accessible to the public via a government website.