Novolak/polyhydroxystyrene copolymer and photoresist compositions

A novolak/polyhydroxystyrene copolymer having a structure as shwon in formula (I), in which R = H, -CH3, -CH2CH3 or -CH2CH2CH3, n = 2 to 15, a process for producing such a copolymer, a photoresist composition containing such a copolymer, a process for producing such a photoresist and a process for producing a semiconductor device using such a photoresist.