I've assumed that, as in the rule for the Riverenza grave, and in keeping with all other descriptions of a riverenza that I am aware of, the passo naturale strisciato is done backwards.
The reverenza semigrave is done in the time of four beats, divided into four parts; in the first beat, do a passo naturale strisciati, in the second and third beats, separate the knees a little, a little lowering the body, and raising the heel of the left foot, which you will find behind; in the fourth, and last, raise yourself, and return with the left foot even, or indeed forwards, in passo naturale. Note that this return into passo naturale is for the galliard, and when you return with the feet even, it is in balletti. It is so called because it is done in half the time of a grave.