The present disclosure relates to a solid-state image sensor, driving method, and electronic apparatus, capable of achieving reduction in pixel size and sensitivity improvement. The solid-state image sensor includes a PD configured to convert light into electric charge by photoelectric conversion and to store the electric charge, a first transfer transistor configured to read out the electric charge stored in the photoelectric conversion unit, a multiplication region configured to store temporarily and multiply the electric charge read out through the read-out unit, and a second transfer transistor configured to transfer the electric charge stored in the multiplication region to a conversion unit configured to convert the electric charge into a pixel signal. Then, an intense electric field is generated in the multiplication region to multiply electric charge by the avalanche effect in transferring the electric charge from the multiplication region to an FD portion through the second transfer transistor. The present technology is applicable to, in one example, the stacked CMOS image sensors.