A new ion-selective membrane composition for ion sensors based on aliphatic urethane diacrylate oligomer is presented. The membrane can be deposited and photolithographically structured on a wafer containing ion-sensitive field effect transistors (ISFETs). Compatibility of the polymer matrix with various plasticizers commonly used in polyvinyl chloride-based ion-selective membrane formulations has been established, and it is shown that the membrane may hold more than 50% of different plasticizers. The photopolymerization rate was found to be higher than for the other compositions used for this purpose. Characteristics of an ammonium ISFET with the developed membrane are presented, the sensitivity was found to be 55 to 59 mV per concentration decade and the range of linear response was from 10-1to 5. 10-5MNH4Cl. © 1994, The Electrochemical Society, Inc. All rights reserved.