  Studying our semirelativistic potential model and the numerical results,
which succeeds in predicting and reproducing recently discovered higher
resonances of $D$, $D_s$, $B$, and $B_s$, we find a simple expression for the
mass gap between two spin multiplets of heavy-light mesons, $(0^-,1^-)$ and
$(0^+,1^+)$. The mass gap between chiral partners defined by $\Delta
M=M(0^+)-M(0^-)$ and/or $M(1^+)-M(1^-)$ is given by $\Delta
M=M(0^+)-M(0^-)=M(1^+)-M(1^-)\approx \Lambda_{\rm Q}-m_q$ in the limit of heavy
quark symmetry, and including $1/m_Q$ corrections, we have $\Delta M\approx
\Lambda_{\rm Q}-m_q+(1.28\times 10^{5}+4.26\times 10^{2}\cdot m_q)/m_Q$ with
$\Lambda_{\rm Q}\approx 300$ MeV, a light quark mass $m_q$, and a heavy quark
mass $m_Q$. This equation holds both for $D$ and $D_s$ heavy mesons. Our model
calculations for the $B$ and $B_s$ also follow this formula.
