Abstract: A semiconductor processing apparatus is disclosed. The semiconductor processing apparatus may include: a reaction chamber comprising an upper chamber wall and a lower chamber wall connected by vertical sidewalls, the chamber walls being joined by an upstream inlet flange and a downstream outlet flange wherein a longitudinal direction of the chamber extends from the inlet flange to the outlet flange and a plurality of ribs provided on an outer surface of at least the upper chamber wall, the plurality of ribs being orientated transversely to the longitudinal direction of the chamber. The semiconductor processing apparatus may also include at least one array of heating elements disposed above the reaction chamber and at least one variable positioning device coupled to the at least one array of heating elements and configured to controllably adjust the position of the at least one array of heating elements relative to the position of the plurality of ribs.