CdTe radiation detectors have been fabricated in a new M-pi-n structure that provides very effective blocking for the leakage current and, as a result, excellent spectral responses are achieved. An iodine-doped n-CdTe layer was grown on the Te-faces of the (1 1 1)-oriented high-resistivity (similar to 10(9) Omega cm) rho-type CdTe wafers at the low substrate temperature of 150 degrees C. An aluminum electrode was evaporated on the n-CdTe side, while a gold electrode was evaporated on the other side. Low leakage current around 60 pA/mm(2) was typically attained for a 0.5 mm thick detector at room-temperature (25 degrees C) for an applied reverse bias of 250 V. Improved charge collection efficiency and spectral responses for different radioisotopes in the energy range of a few tens of keV to several hundreds of keV were obtained due to the application of very large electric fields on the detectors. The performance of the detectors thus fabricated is presented.