A method for fabricating thick film alumina structures used in high frequency, low loss applications is provided. More particularly, the invention is directed to a co-fire process for fabricating, or laminating, thick film structures to one another by printing a conductor layer between two thick film circuits, drying the layer, and co-firing the combined structure. This process is particularly useful in fabricating high frequency (e.g. 10 gigabit) fiber optic transmitters.