Ultrathin c-Si solar cells with their active layer thicknesses ranging from a few micrometers to several tens of micrometers will play a very important role in reducing the material costs of industrial c-Si solar cells. This work presents a new high efficiency light trapping scheme (HE-LTS) with two cavities for ultrathin c-Si solar cells. By analyzing the variations of the important optical parameters of each light trapping unit with its geometric parameters, the light trapping performances of the HE-LTS have been optimized. The results show that the light trapping abilities of the HE-LTS can exceed obviously that of Lambertian LTS in a broad range of geometric parameters for both TE and TM modes; the photocurrent densities of an ultrathin c-Si solar cell with the optimal HE-LTS can reach 36.65 mA/cm(2) and 40.47 mA/cm(2) for the TE and TM modes, respectively.