To provide an isolator without requiring a magnet by forming the isolator through the use of a ferrite having an inner magnetic field and mounting it on a microwave integrated circuit or a microwave circuit module in a surface mounting form together with a semi-conductor chip.

The isolator 10 is formed by using the ferrite provided with the inner magnetic field itself without requiring an outer magnetic field and the isolator 10 is mounted on the microwave integrated circuit or the microwave circuit module in the surface mounting form together with the semi-conductor chip. The hexagonal-type crystal structured ferrite 1 is calcined columnarly so as to be embedded in a ceramic substrate 5. Then, a whole surface grounded conductive layer 7 is formed on one surface of the ceramic substrate 5. On the other surface, branch lines 2 and 3 extended from the input/output ends of the surface mounting-type isolator 10, a contact surface 4 for connecting the branch lines 2 and 3 and a terminating resistance 6 connected to the contact surface 4 so as to be terminated are formed in the pattern.