Provided herein is a PIN diode, a manufacturing method thereof, an x-ray detector using the PIN diode, and a manufacturing method thereof, the PIN diode manufacturing method according to an embodiment of the present disclosure including forming a lower electrode layer, and forming a lower electrode by etching the lower electrode layer; depositing a PIN layer for formation of a PIN structure above the lower electrode, and depositing an upper electrode layer for formation of the upper electrode above the PIN layer; forming a photo resist pattern above the upper electrode layer, and forming the upper electrode by etching the upper electrode layer having the photo resist pattern as a mask; forming the PIN structure by etching the PIN layer; etching an edge area of the upper electrode having the photo resist pattern as a mask; and removing the photo resist pattern.