Women’s underrepresentation in science, technology, engineering, andmathematics (STEM) is related to the hierarchical social structure of genderrelations in these fields. However, interventions to increase women’sparticipation have focused primarily on women’s interests rather than on STEMmanagers’ hiring practices. In this research, we examine STEM hiringpractices, explore the implicit bias in criteria used by STEM managers, andsuggest possible corrective solutions. Using an experimental design with 213men and women STEM managers, we show that when evaluating a female candidate,women and men STEM managers apply differential selection criteria, with mendemonstrating implicit in-group gender favoritism in their hiring decisions.Specifically, the ability to work long hours was a more important criterionfor male managers when evaluating a female candidate, forming an implicitgender bias, whereas female managers gave greater importance toproblem-solving ability, a more gender-equal criterion. Adding a personalnote to the curriculum vitae stating that the candidate had hired a full-timenanny was useful in decreasing the importance of the ability to work longhours criterion for men managers. We suggest individual and institutionalinterventions to reduce this bias, as a path to increasing women’sparticipation in STEM.