Handheld electronic devices including motion sensing and processing. In one aspect, a handheld electronic device includes a set of motion sensors provided on a single sensor wafer, including at least one gyroscope sensing rotational rate of the device around at least three axes and at least one accelerometer sensing gravity and linear acceleration of the device along the at least three axes. Memory stores sensor data derived from the at least one gyroscope and accelerometer, where the sensor data describes movement of the device including a rotation of the device around at least one of the three axes of the device, the rotation causing interaction with the device. The memory is provided on an electronics wafer positioned vertically with respect to the sensor wafer and substantially parallel to the sensor wafer. The electronics wafer is vertically bonded to and electrically connected to the sensor wafer.