This paper presents an analytical model of the optical sensitivity and dark current of thin film SOI PIN diodes validated by measurements. This allows us to prove the very good adequacy of thin film SOI for UV-sensing (quantum efficiency in excess of 60% without any anti-reflection coating and dark current lower than pA for a total diode area of 50 x 50 mu m(2)) and to propose a new method for extracting the effective lifetime and electron, and hole mobilities in SOI thin film ungated structures. (c) 2007 Elsevier Ltd. All rights reserved.