Developed by Tom Oberheim, they were the first production synthesizers capable of playing chords.

[1] In late 1975, after Norlin canceled several large Maestro orders, Oberheim developed a series of polyphonic synthesizers by combining multiple SEMs with a digitally-scanned keyboard developed by Dave Rossum and a two-channel sequencer.

In 1976, Oberheim introduced the Polyphonic Synthesizer Programmer (PSP-1), an optional module which made possible the storage and recall of most of the SEM's parameters, as well as the ability to glide from one note or chord to another using portamento.

[2][3] In 1977, the Oberheim Eight Voice (EVS), available with either a single or dual manual keyboard, was added to the series.

[1] Despite their maintenance cost and rarity, Oberheim Polyphonic Synthesizers are still adored by many musicians today for their characteristic sonic 'thickness' and 'depth' caused in part by the random variance between each SEM module.