A negative photoresist has been developed by partial esterification of poly(p-hydroxystyrene) withp-azidobenzenesulfonyl chloride. About 10% of esterification is sufficient to sensitize the polymer to light in the wavelength region between 240 and 300 nm. The dose required to insolubilize the polymer was 80 mJ/cm2. The resolution capability is not as high as expected because of the swelling of photoinsolubilized resist films in an aqueous alkaline developer.