Listbox Size

I have a drop-down with 40 option values and only one option should be selected of the 40 options. The list size should be 1.

When I click on the list, it drops down 30 options (a very long list) with a scrollbar for the last 10 options.

Is there any way, when I click on the list it drops down only 5 options (as if the list is of size 5) and allow a scrollbar to browse the remaining 35 options.

Code is:
<select name="deplist" id="deplist"
<option value="Commerce">Commerce</option>
<option value="Instru">Instrumentation</option>
... similar such 38 options
</select>