A piezoelectric transformer comprising a rectangular plate of a piezoelectric material which is polarized in a thickness direction in a first half section of the plate in a longitudinal direction but is polarized in a width direction in a second half section of the remaining half section. A pair of primary electrodes are coated on the upper and the lower surfaces of the first half section and a pair of secondary electrodes are coated on the opposite side surfaces of the second half section, in an alternative structure, the plate is polarized in the thickness direction in opposite end sections of the plate having a size one third of length of the plate and polarized in width direction at the remaining middle section of plate between opposite end sections. The pair of primary electrodes formed on upper and lower surfaces of opposite end sections of plate and pair of secondary electrodes formed on opposite side surfaces of middle section. The pair of secondary electrodes may be deposited on upper or lower surfaces adjacent opposite side edges. In a voltage converter using the piezoelectric transformer, a pulse generator generates two voltage pulse signals having frequency equal to resonance frequency of transformer but being reverse to each other in phase, which signals are applied to primary electrodes, respectively to produce high voltage AC output across secondary electrodes isolated from primary electrodes.