This paper studies gender wage differentials by providing a maximum likelihood structural estimation of the frictional parameters of an equilibrium search model with on-the-job search and firm heterogeneity. In a second step, I also consider the role of discrimination. Results indicate higher level of search frictions for women, this result is confirmed by various robustness checks, and by different specification and estimation strategies. I also find that the resulting mapping from productivity to wages for men is highly non linear, while for women it is almost linear. Search, productivity, and discrimination play different roles in shaping the gender differential depending on the specification and estimation of the model.