A Si-YBaCuO intermixed system has been formed using rapid thermal annealing (RTA) of Cu/BaO/Y2O2/Si layered structures, which were deposited on MgO substrates by electron-beam evaporation. The electrical and structural properties of the Si-YBaCuO system have been analyzed by resistivity, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy and Auger depth profiling measurements. It was found that Si mixed with YBaCuO during annealing, thus creating an insulating film. This effect has been used to pattern YBaCuO films. The patterning process was carried out on an underlying silicon layer, rather than the YBaCuO film itself, using conventional photolithography or laser etching. After YBaCuO film deposition and RTA, the patterned region became superconducting separated by Si-YBaCuO intermixed areas. Micron-sized line features with Tc's above 77 K have been demonstrated.