Magnetic sensor

To provide a compact Hall element which has high magnetic sensitivity and a wide measuring range and which is resistant to application conditions such as high temperatures or radiations, a micro-vacuum-tube type Hall element is proposed. A rectangular recess (7) is formed in a surface layer of an insulator layer (10). A negative electrode (1) for emitting electrons and a positive electrode (2) for collecting the electrons are provided on the surface of the insulator layer surrounding the recess with the recess interposed therebetween. A gate electrode (3) is provided on the bottom of the recess so that it faces the negative electrode. Hall electrodes (4) are provided on the surface of both sidewalls which are parallel with the line connecting the centers of width of the negative and positive electrodes. All of these electrodes are disposed in a vacuum.