Provided are a method of forming a conductive layer on an inner portion of a through-electrode in which uniform adhesion property of plating in the inner portion of a through-hole is enhanced and a tact time is short, and a semiconductor device. The method of forming a conductive layer includes: a first plating step of forming a first plating layer on the inner portion of the through-hole; a plating suppression layer forming step of forming a plating suppression layer including a material different from a material of the first plating layer in an opening portion of the through-hole after the first plating step; and a second plating step of forming a second plating layer by plating on the inner portion of the through-hole after the plating suppression layer forming step.