Two types of carbon nanotubes (MWCNTs and SWCNTs) films were used tofabricate hydrogen gas sensors. CNTs films were deposited on porous silicon substrate by the drop casting method. The two sensors showed high sensitivity to hydrogen gas at different concentrations. Experimental results indicated that the SWCNTs have a better performance than MWCNTs. The SWCNTs gas sensor shows high sensitivity at 150oC with 29sec response time, whereas MWCNTs gas sensor shows best sensitivity at 200oC with 24sec response time.