The paper presents the study of experimental current responses of Si p+-n-n+ 3 mm thick structure operated at 40 mK. Analysis of the data showed reduction of carrier lifetimes in silicon to 50‒70 ns for electrons and 350 ns for holes, which is the most critical factor for restriction of the internal thermal gain in bolometric detectors based on the Joule-Lenz effect and should be accounted for in the optimization of detector design.