The authors have developed gas sensors that operate when gas flowing through carbon nanotube (CNT) channels is adsorbed on the inner surface of the channels. CNTs fabricated on anodic alumina membranes were used. The CNTs are well ordered and connected in parallel, forming parallel channels. The sensors are highly responsive to NH3 and NO2 molecules and the response times are relatively short. They are completely recovered within 10min when a dc voltage of 10V is applied for 2min. The fabrication processes are relatively simple and do not require special techniques such as e-beam lithography.