With this semiconductor device, the distortion and cracking of a thinned portion of a semiconductor substrate are prevented to enable high precision focusing with respect to a photodetecting unit and uniformity and stability of high sensitivity of the photodetecting unit to be maintained. Accordingly, processes for selective gas separation of a gas mixture are provided in which a gas mixture is contacted with such a membrane such that a selective portion of the gas mixture passes through the membrane. The apparatus usefully includes a mode select device operable by the participant at a given station to designate each of a succession of chat content segments generated at the given station to be either for unrestricted use, or for off the record use, selectively.