A semiconductor apparatus includes first, second and third transistors integrated in a monocrystal chip. Both the first and second transistors are vertical devices, each having a source node, a gate node and a drain node. The source node of the first transistor electrically connects to a primary source pin, the source node of the second transistor to a sample pin, and the gate nodes of the first and the second transistors to a control-gate pin. The third transistor is a vertical JFET with a source node, a control node and a drain node. The source node of the third transistor electrically connects to a charge pin, and the control node of the third transistor to a charge-control pin. All of the drain nodes of the first, second and third transistors are electrically connected to a high-voltage pin.