Method of manufacturing semiconductor device

Gate electrodes are formed in a high speed transistor forming region, a low leakage transistor forming region, and a medium voltage transistor forming region, respectively. Thereafter, a photoresist film covering the medium voltage transistor forming region is formed. Then, ions of an impurity are implanted into a semiconductor substrate while using the photoresist film and the gate electrodes as a mask, and p-type pocket regions, extension regions, and impurity regions are thereby formed. Subsequently, another photoresist film covering the high speed transistor forming region is formed. Then, ions of an impurity are implanted into the semiconductor substrate while using the other photoresist film and the gate electrodes as a mask, and impurity regions and extension regions are thereby formed.