Archive for custom taxonomy lists all posts instead of current taxonomy

You have a syntax error in your query. According to the documentation for WP_Query, tax_query is an array of arrays of parameters, which is to say that it should probably look like this:

'tax_query' => array(
    array(                     
        'taxonomy' => 'semester',
        'field' => 'slug',
        'terms' => $getterm,
        'include_children' => true,          
        'operator' => 'IN' 
    ),
),