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In his 2000 lecture, Jack St. Clair Kilby describes an August 1958 comparison circuit made from separate silicon elements. Resistors were cut and etched; capacitors came from diffused, metallized semiconductor wafers. It tested whether semiconductor elements could perform all the required functions, but was still a discrete circuit. For the September prototype he used already diffused germanium material with contacts, cut into bars, and hand-applied wax masks to define a transistor and a distributed resistor-capacitor region. Applying supply power produced an oscillation.^[ref]

An inspected eyewitness interview describes the germanium on a microscope slide with protruding wires; changing its connections changed the oscilloscope display from a straight line to a sinusoid. This supplied a qualitative connected/disconnected comparison, not a calibrated record of amplitude, loading or repeatability.^[ref]

The inference was feasibility: integrated semiconductor elements could cooperate as an operating electrical circuit. The hand-wired germanium prototype did not yet supply the deposited integrated circuit interconnects of Robert Noyce's silicon design. Nor does a working prototype establish manufacturing yield or long-term reliability.

A monolithic integrated circuit has its circuit elements fabricated in or on one semiconductor die. Their connections are essential: an unconnected collection of transistors does not implement the intended electrical circuit.

An original ideal example separates function from fabrication. Connect two resistors, $R_1=10\mathrm{k\Omega }$ above $R_2=20\mathrm{k\Omega }$, in a series circuit across an ideal $3\mathrm{V}$ voltage source. With no load electric current drawn from their meeting point, Ohm's law and the Kirchhoff cycle law giveThese equations apply to either a discrete circuit or an idealized monolithic integrated circuit realizing those same electrical resistances. Integration changes construction; the electrical circuit equations still determine the output. A real load, unwanted capacitance or finite resistor tolerance changes the ideal calculation. Manufacturing many functions together also couples their fate: a fatal defect can discard an entire semiconductor die, motivating the Poisson defect yield model.