Current‐voltage characteristics from 140° to 350°K are measured on a longp+‐&pgr;‐n+silicon structure biased into the double‐injection regime. The I‐V characteristics obey aJ∝V2/L3relation throughout the considered temperature range, and the magnitude of the double‐injection current is predicted within 10% by the Lampert expressionJ= (9/8)q&mgr;p&mgr;n&tgr; (p0‐n0)V2/L3. The transient response of double injection as analyzed by Baron provides a direct measure of the common high‐level lifetime &tgr;, which is given by the formula &tgr;=30.7×10−6(T/298)1.93±0.23sec. Conductivity, Hall effect, and the large‐signal‐step‐response method of Dean establish the electron and hole mobility as &mgr;n=1280 (298/T)1.75±0.31cm2/V‐sec and &mgr;p=410 (298/T)2.18±0.04cm2/V‐sec, respectively, for 140°≤T≤350°K. The consistency between the measured values of the lifetime and mobilities with values reported by the literature establishes that the temperature dependence of a long double‐injectionp+‐&pgr;‐n+silicon device is in agreement with the Lampert expression and the temperature variation of &tgr; (T), &mgr;p(T), and &mgr;n(T). A 14‐MeV neutron irradiation of 1.25×1011n/cm2does not alter the quadratic lawJ∝V2/L3of the device but results in lower current levels when compared to the preirradiation condition. Pulse and dc measurements analogous to the preirradiated case give&tgr;ˆ=8.9×10−6(T/298)0.68±0.07 sec,&mgr;ˆp=385(298/T)1.30±0.10 cm2/V−sec, and&mgr;ˆn=1160(298/T)1.28±0.21 cm2/V−secfor the carrier lifetime and mobilities, respectively. After irradiation reasonable agreement is found between the measured double‐injection current and that predicted from Baron's first‐order correction of the Lampert expression for diffusion and thermal generation effects.