Abstract: A polishing endpoint detecting device of a polishing apparatus detects a polishing endpoint of a polishing process by measuring light reflected from a surface of a semiconductor substrate being polished. The apparatus also includes a polishing pad and a rotary plate each of a light-transmitting material. The light is directed onto the surface of the semiconductor substrate through the polishing pad and the rotary plate and is scanned across the surface of the semiconductor substrate along a horizontal line which passes through the centers of the polishing pad and the semiconductor substrate. A light-measuring instrument measures a characteristic of the light reflected from the surface of the semiconductor substrate, and a processor detects the polishing endpoint by analyzing signals produced by the light measuring instrument.