The time-of-flight (TOF) transient photoconductivity technique is used with an appropriate method and algorithm, based on the time dependence of the transient photocurrent i(t), to probe the spatial distribution of x-ray induced net bulk space charge in stabilized a-Se (a-Se:0.3%As doped with 10 to 20 ppm Cl) x-ray photoconductors with long carrier lifetimes (hole lifetime of ∼500 μs and electron lifetime of ∼750 μs from interrupted TOF). It is observed that x-ray irradiation of biased a-Se photoconductors results in a net negative space charge distribution. The spatial variation of the space charge density ρ(x) was found to decay exponentially from the irradiation surface. The spatial dependence of ρ(x) did not follow the photon absorption profile as closely as observed previously when only unbiased a-Se layers were irradiated. However, the changes in the spatial distribution of ρ(x) with the x-ray mean photon energy exhibited the same tendency as the photon absorption profile. The distribution of the trapped charge and rate of detrapping was examined as a function of temperature, photon energy, and with infrared illumination. The total negative space charge was found to decrease with time following a power law dependence of the form N∼t−n, where n≈0.3 and was independent of the irradiation intensity, which indicates that electron detrapping occurs from an energy distribution of deep localized states. Using an infrared (IR) filter that allows photon energies smaller than 1.1 eV to pass, it is shown that IR illumination increases the rate of detrapping and confirms that electrons are trapped in deep electron trapping states between 0.6 and 1.1 eV in the density of states diagram of a-Se [M. Abkowitz Philos. Mag. Lett. 58, 53 (1988)]. The mean detrapping current was found to be ∼10 pA, orders of magnitude smaller than the expected dark current. However, the trapped charge modifies the electric field at the top metal electrode causing it to become more injecting and leading to an increase in the dark current. The increase in the dark current is a possible origin for the persistent x-ray photocurrents recently reported for a-Se x-ray photoconductors.