A method of fabricating a photomask includes providing a mask blank; removing a portion of the resist layer to form a patterned resist layer exposing a portion of the cooling layer; patterning the cooling layer by using the patterned resist layer as an etching mask; patterning the opaque layer; and removing the patterned resist layer and the patterned cooling layer. The mask blank includes a light-transmitting substrate and an opaque layer, a cooling layer, and a resist layer sequentially stacked thereon, wherein the cooling layer has a thermal conductivity ranging between 160 and 5000 and an effective atomic number ranging between 5 and 14.