The transformer has a ceramic body (3), which comprises two functional parts (5, 7) and an insulation area (10), which mechanically connects the functional parts. Passages (1, 2) are formed in the body and penetrate through both the functional parts and the insulation area. The passages extend in a longitudinal direction of the body, where each functional part has alternatively arranged inner electrodes (4a, 4b, 8a, 8b), which are aligned perpendicularly to the longitudinal direction. A filling material or a passivation layer (12) is arranged in each of the passages. An independent claim is also included for a method for manufacturing a piezoelectric transformer.