The evaporation boat comprises superposed upper and lower sheets. The upper sheet includes a upwardly convexed central section and a pair of side sections bent back toward the central section and the lower sheet includes a downwardly convexed central section and a pair of side sections bent inwardly toward the upper sheet. The upper and lower sheets are superposed each other such that the central sections of the upper and lower sheets define a substantially closed chamber for accomodating source material to be evaporated, that slit shaped vapor passages are formed between the upper and lower sheets or the opposite sides of the chamber and that any straight line drawn between any point on the surface of the source material and any point in the passages intersects the inner wall of the upper or lower sheets.