A process to manufacture a semiconductor optical modulator is disclosed, in which the process easily forms a metal film including AuZn for the p-ohmic metal even a contact hole has an enhanced aspect ration. The process forms a mesa including semiconductor layers first, then, buries the mesa by a resin layer sandwiched by insulating films. The resin layer provides an opening reaching the top of the mesa, into which the p-ohmic metal is formed. Another metal film including Ti is formed on the upper insulating film along the opening.