Organic field-effect transistors (OFETs) have received increasing attentions, and their performances have been improved significantly and become comparable to those of amorphous silicon transistors. One of the potential applications of OFETs is chemical sensing. Herein, we would like to present the applications of OFETs, which are based on two organic conjugated small molecules, for sensing chemical vapors. Thin film OFETs with a tetrathiafulvalene (TTF) derivative with an electron-withdrawing benzothiadiazole moiety exhibited good hole mobility up to 0.73 cm2V-1s-1 and high on/off ratio up to 105. More importantly, it was successfully utilized for sensing chemical vapors of DECP or POCl3 (down to10 ppb)which are simulants of phosphate-based nerve agents. In order to further improve the OFET-based sensor’s selectivity, we designed and synthesized another compound with 2-methylenemalononitrile structure, which can react with H2S quickly. By utilizing the chemical reactions, OFET-based sensor for H2S with high selectivity and sensitivity down to ppb levels was developed. In addition, it was found to be highly emissive in the solid state, and the microrods exhibited outstanding optical waveguide behaviors.