The TST-9 Junior was a development of the TST-7 Junior touring motor glider, incorporating a T-tail and other design refinements. The 12.41NaN1 span, shoulder-mounted wing is slightly forward-swept. The wing has less span than the TST-7 Junior and consequently the aircraft has a lower glide ratio. The landing gear is of tricycle configuration, making taxiing the aircraft much easier than the monowheel gear used on the TST-1 model. The aircraft was later further refined into the TST-13 Junior.
The price for a completed ready-to-fly aircraft in 2004 was €22,240.