The company's market share has fallen by 40%, making Hewlett-Packard the top Unix server supplier.
The latest figures from research firm IDC reveal that the total Unix server market has declined in revenue terms by 28% on the same quarter last year.
HP had the highest revenue from servers shipped, capturing 28% of the market, followed by Sun with 25.1%. IBM was third with 19.4%; Compaq came fourth with 11.4% and Fujitsu Siemens was fifth with an 8.7% share of the market.
Nancy Taylor, senior research analyst for Unix and mid-range server research at IDC, said the decline of Unix was the result of a freeze in spending on non-essential infrastructure by the telecom and finance sectors. She said that both HP and Sun had large numbers of users in these two industries.
"The economic downturn, 3G licence overspend and a general drop in business confidence among global customers have all had a massive effect on demand for Unix servers," she added.