If $l_1, l_2, l_3$ are the lengths of the emitter, base and collector of a transistor, then -

$l_1 = l_2 = l_3$ $l_3 < l_2 > l_1$ $l_3 < l_1 < l_2$ $l_3 > l_1 > l_2$

$l_3 > l_1 > l_2$

From basic knowledge, $l_2$ is least.Thickness of base is least