When A.J.N. Boosten died unexpectedly during an operation on the 2nd of Januari 1951 at the age of 57,  he was at the height of his career. Several of his churches were under construction at that time, while he had been designing several new ones until shortly before his death. After his death several of these designs were completed under supervision of other architects, like Boosten's son Theo. The St. Gemma of Sittard however was built by H.J. Palmen.
The St. Gemma is a remarkable bulding with a asymmetrical nave with a large rose-window, behind a wide portal. On the north side of the aisle is the church's only, but rather wide, side-aisle which, as often with Boosten's churches, has a flat roof.  A monumental eastern part contains the choir and is crowned by two spires. At the back, a  bulge in the centre of the wall serves as an apse.