We have studied the solubilities of photodegraded positive photo resist systems such as AZ*1350, AZ*2400 and AZ*111 resists by using in situ resist film thickness measurement techniques. The photo resist films were exposed at the sensitive wavelength of 0.4047 pm at several exposure dosage levels. The aqueous developer systems used with the above resists were AZ* developer, undiluted; AZ*2401, diluted with DI water (1:4); and AZ*303, diluted with DI water, (1:5), respectively. Published analytical dissolution rate models describe a linear relation between film thickness lost versus development time for unexposed and uniformly exposed resist films. We present results that demonstrate the prebaked resist film dissolution are not, in general, linear in time. Also, the dissolution behaviors are different with the different resist-developer systems we studied. Furthermore, the optical exposure effects are different from resist to resist in a manner that can be explained by the photoresponse of the resists at the exposure wavelength.