A transformer of fully symmetric structure includes a primary coil assembly and a secondary coil assembly. The primary coil assembly includes a plurality of primary coils formed in a plurality of metal layers, and a first interlayer connection unit for connecting the primary coils. The secondary coil assembly includes a plurality of secondary coils formed in the plurality of metal layers, and a second interlayer connection unit for connecting the secondary coils. The primary and secondary coils formed in the same metal layer are concentric and axisymmetric with respect to a diameter line passing through a planar center point. A balanced-unbalanced transformer (balun) is a type of transformer that may be used to convert an unbalanced signal to a balanced one or vice versa. An integrated circuit may include a semiconductor substrate and a transformer. Electrical elements such as transistors may be formed on the semiconductor substrate.