He gets up part of stairs (5)
I believe the answer is:
riser
This clue is a double definition.
'he gets up' is the first definition.
(I've seen this before)
'part of stairs' is the second definition.
('riser' is part of 'stairs')
(Other definitions for riser that I've seen before include "Upright part of step - vertical pipe" , "Vertical upward pipe" , "person advancing position?" , "Front of a staircase step" , "Face of a step" .)