Fabrication methods are provided for microchips that control both the rate and time of release of multiple chemical substances and allow for the release of a wide variety of molecules in either a continuous or pulsatile manner. In all of the preferred embodiments, a material that is impermeable to the drugs or other molecules to be delivered and the surrounding fluids is used as the substrate. Reservoirs are etched into the substrate using either chemical (wet) etching or plasma (dry) etching techniques well known in the field of microfabrication. Hundreds to thousands of reservoirs can be fabricated on a single microchip using these techniques. A release system, which includes the molecules to be delivered, is inserted into the reservoirs by injection, inkjet printing, or spin coating methods. Exemplary release systems include polymers and polymeric matrices, non-polymeric matrices, and other excipients or diluents. The physical properties of the release system control the rate of release of the molecules. The reservoirs can contain multiple drugs or other molecules in variable dosages. The filled reservoirs can be capped with materials that passively disintegrate, materials that allow the molecules to diffuse passively out of the reservoir over time, or materials that disintegrate upon application of an electric potential. Release from an active device can be controlled by a preprogrammed microprocessor, remote control, or by biosensors.