Delocalized singlet biradical hydrocarbons hold promise as new semiconducting materials for high-performance organic devices. However, to date biradical organic molecules have attracted little attention as a material for organic electronic devices. Here, this work shows that films of a crystallized diphenyl derivative of s-indacenodiphenalene (Ph-2-IDPL) exhibit high ambipolar mobilities in organic field-effect transistors (OFETs). Furthermore, OFETs fabricated using Ph-2-IDPL single crystals show high hole mobility ((h) = 7.2 x 10(-1) cm(2) V-1 s(-1)) comparable to that of amorphous Si. Additionally, high on/off ratios are achieved for Ph-2-IDPL by inserting self-assembled monolayer of alkanethiol between the semiconducting layer and the Au electrodes. These findings open a door to the application of ambipolar OFETs to organic electronics such as complementary metal oxide semiconductor logic circuits.