Published online by Cambridge University Press: 07 September 2020
Let
$\mathcal A$
and
$\mathcal B$
be commutative and semisimple Banach algebras and let
$\theta \in \Delta (\mathcal B)$
. In this paper, we prove that
$\mathcal A\times _{\theta }\mathcal B$
is a type I-BSE algebra if and only if
${\mathcal A}_e$
and
$\mathcal B$
are so. As a main application of this result, we prove that
$\mathcal A\times _{\theta }\mathcal B$
is isomorphic with a
$C^*$
-algebra if and only if
${\mathcal A}_e$
and
$\mathcal B$
are isomorphic with
$C^* $
-algebras. Moreover, we derive related results for the case where
$\mathcal A$
is unital.