Hexamethyldisiloxane (HMDSO) was deposited on a gate dielectric surface by plasma enhanced chemical vapor deposition for surface treatment, and its effects on the microstructure of pentacene and the transistor characteristics were examined. HMDSO films were deposited at room temperature at various RF powers (10 W to 120 W). Atomic force microscopy analysis of the pentacene films showed a significant increase in the grain size of the samples treated under the optimum RF power (10 W), which in turn led to a significant improvement in the electrical mobility. These results show that PECVD-grown HMDSO can be used as an effective surface treatment and warrants further investigation for process optimization. (C) 2009 Elsevier B.V. All rights reserved.