Organic field-effect transistors were fabricated where the active semiconductor layer consisted of a co-evaporated film of pentacene and a perylene derivative, N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide. The device characteristics were evaluated in an oxygen-free environment. The field-effect transistor showed excellent ambipolar operation with field-effect hole mobility of 0.09 cm(2) V-1 s(-1) and field-effect electron mobility of 9.3 x 10(-3) cm(2) V-1 s(-1). The threshold voltage for p-channel operation was -18 V and the same for n-channel operation was 15 V. This ambipolar device could be a building block to form flexible integrated circuits with low-power consumption and ease of design. (c) 2006 Elsevier B.V. All rights reserved.