Numerical study of boiling phenomena in planar jet impingement is conducted by solving the conservation equations of mass, momentum and energy. The liquid-air interface as well as the liquid-vapor interface with phase change is tracked by a sharp-interface level-set method. The computational results demonstrate that the predicted heat flux is in good agreement with the experimental data. The effects of bubble nucleation period and density on bubble growth and heat transfer in jet impingement boiling are investigated.