In this paper, we propose a new hybridizable discontinuous Galerkin (HDG)
method for steady-state diffusion problems. In the proposed method, both the
trace and flux of the exact solution are hybridized, whereas only the trace is
hybridized and the flux is approximated by the numerical flux. We prove that
our method is superconvergent if finite element spaces admit the
$M$-decomposition. The so-called Lehrenfeld-Sch\"oberl stabilization is
implicitly included in our method, so that the orders of convergence in all
variables are optimal without postprocessing and computation of any projection
if finite element spaces are appropriately chosen. Numerical results are
present to validate our theoretical results.