Abstract: This paper presents design, computer analysis and experimental result of laminar flow electron beam with rectangular cross section. The beam is used in a deflection-modulated electron-bombarded semiconductor amplifier. This kind of amplifier is a new device in microwave field developed during the last decade.Owing to employing special correcting lens, laminar flow beam with rectangular cross section of 13 mm2 is obtained. Using correcting lens to obtain rectangular beam of finite width is a useful method.This method may be applied to other fields.