Microsensor for nitrogen dioxide (NO2) fabricated by Langmuir-Boldgett (LB) films of Samarium bis[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] complex Sm[Pc*](2) (Pc* = Pc(OC8H17)(8)) and charge-flow transistor (CFT) are evaluated. Pure Sm[Pc*](2) and mixture of Sm[Pc*](2) and octadecanol (OA) deposited from both pure water and 10(-4) M Cd2+ subphases were investigated. It is found that a mixture of 1:3 Sm[Pc*](2):OA forms an excellent material for the fabrication of gas-sensing LB film by studying the film-forming characteristic. Such novel microsensor has been fabricated by incorporating the multilayer LB film into the gate electrode of a metal-oxide-semiconductor field effect transistor, forming an array of CFT. On the application of a gate voltage (V-GS), greater than the threshold voltage (V-TH), a delay was observed in the response of the drain current. It is due to the time taken for the resistive gas-sensing film to charge up to V-GS. This delay characteristic was found to depend on the concentration of NO2. Results are presented showing that the device can detect reversibly concentration of NO2 gas down to 5 ppm at room temperature.