Beechjet 400
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance
Flight Crew Landed in Emergency Condition
Aircraft
As we started descending into ZZZ we noticed the hydraulic gauge went up past red line (High hydraulic pressure). Pulled out the checklist and as per the checks performed a hydraulic system relief which had us do an manual gear extension; no flap landing and power brake failure landing. Went to a hold at ZZZZZ intersection to finish our manual gear extension checklist and then continued to ZZZ for a no flap ILS  to XXR and landed without incident.Hydraulic over pressure. Cause unknown.
Flight crew flying BE-400 aircraft reported hydraulic malfunction on descent. Landed at destination without incident.