Stefan Martis was a pilot who at least flew the Avia B-534 during the Second World War. No confirmed kills have been found for him while flying the Avia B-534.
At dawn of 24 March 1939, while he was on a ground-attack mission with two other pilots, when they were attacked by Hungarian Fiat CR.32’s. Desátnik (Corporal) Martis plane was seriously damaged in the ensuing combat.
On 25 July 1941 Ctk. (Sergeant) Frantisek Brezina’s Avia B-534 was damaged by Soviet AA fire and he was forced to land behind enemy lines. He was rescued by Ctk. Stefan Martis who landed alongside and brought him home, clinging to the wing struts!
On 11 September 1943, catár (Sergeant) Alexander Geric and catár (Sergeant) Stefan Martis escorted a German Fw189 reconnaissance aircraft over the Front and did not return. They had originally planned to shoot down the German aircraft, but after landing at Anapa, Stefan Martis informed his base that they had been attacked by Russian fighters and that Alexander Geric’s Bf 109G-4 (w/n 14938 Yellow 2) had been shot down. Moscow Radio even broadcast a report to substantiate the claim and the pilot was posthumously awarded a distinction. Of course, Geric had also fled to the Russians, with radio mechanic Private 1st Class Vincent Tkácik concealed in the fighter’s fuselage - the latter was then able reveal details of a secret radio station to the Russians. In 1944 Alexander Geric was dropped over Slovakia by the Russians to undertake an intelligence mission.
Martis ended the Second World War with a total of 6 victories.

Sources:
Avia B-534 - Jirí Vraný, 1994
Additional information is kindly provided by Pavel Vancata.