The experimentally discovered effect of the negative sensitivity of a double collector bipolar magnetotransistor of n-p n type of which the base is a diffusion well is related to the appearance of the volume magnetoconcentration effect at the well-substrate p-n junction This new effect was investigated with the help of device simulation programs and it was established that the sensitivity sign of the magnetic field is determined by the distribution of flows of electrons and holes at the well-substrate p-n junction Furthermore an analysis of the volume charge modulation of the p-n junction by the magnetic field was conducted (C) 2010 Elsevier Ltd All rights reserved