Abstract. We consider a structural acoustic problem with the flexible wall modeled by a thermoelastic plate, subject to Dirichlet boundary control in the thermal component. We establish sharp regularity results for the traces of the thermal variable on the boundary in case the system is supplemented with clamped mechanical boundary conditions. These regularity estimates are most crucial for validity of the optimal control theory developed by Acquistapace et al. [Adv. Differential Equations, 2005], which ensures well-posedness of the corresponding differential Riccati equations. The proof takes full advantage of the exceptional boundary regularity of the mechanical component of the clamped thermoelastic system as well as of the sharp trace theory pertaining to wave equations with Neumann boundary data.1. Introduction. This paper continues-and concludes-the study initiated in [7], focused on a class of boundary control problems for a system of partial differential equations (PDE) describing fluid-structure interactions (structural acoustic model), which also include thermal effects. Our primary goal is to discuss the question of solvability of the associated quadratic optimal control problems over a finite time interval, along with well-posedness of the corresponding differential Riccati equations (DRE). As it is known and will become clearer later, this naturally leads us to undertake a preliminary investigation of the regularity properties of the solution to a dual (homogeneous) boundary value problem.The structural acoustic model under investigation is the same as in [7], except for the boundary conditions. More precisely, the PDE system (that 2000 Mathematics Subject Classification: 35B37, 35M20, 35B65, 49J20, 93C20.