PURPOSE: To provide a highly fine lead frame capable of dealing with making small the pitch of the tip end of an inner lead and making fine the tip end of the same resulted in increasing pins of a semiconductor device and making the device fine, and also capable of dealing with later processes.

CONSTITUTION: A method is to fabricate a lead frame used for a resin sealed semiconductor device and the like with an etching process. For a lead frame raw material 1 on opposite surfaces of which predetermined resist patterns 2 are formed, there is performed a first etching with a corrosion solution from the opposite surfaces of the lead frame raw material 1, and there is stopped the first etching after one surface side is corroded by a predetermined amount into a flat state. An etching resistive layer 7 having etching resistance is buried in the part corroded into the flat shape, and a second etching is performed from the other surface side to permit the tip end of the inner lead to penetrate the lead frame.