The S&P/ASX 200 Index (ASX: XJO) is on course to start the week with a solid gain. In afternoon trade, the benchmark index is up 0.5% to 8,212.7 points.

Four ASX shares that are rising more than most today are listed below. Here's why they are charging higher:

Alpha HPA Ltd (ASX: A4N)

The Alpha HPA share price 5.5% to 89.7 cents. This morning, the High Purity Alumina (HPA) producer released an update on its semiconductor sector marketing activities. Management notes that these activities are positively impacting both Stage 1 and Stage 2 of the HPA First Project in Gladstone, Queensland. Managing Director, Rob Williamson, said: "The semiconductor sector is a key focus for the Commercial team, with attractive pricing and demand pull from significant AI data centre growth and power electronics. Alpha's technology is enabling our products to outperform in both the CMP slurry and thermal interface packaging applications, which is leading to the recent Letters of Intent we are seeing coming from this space."

Harvey Norman Holdings Ltd (ASX: HVN)

The Harvey Norman share price is up 3.5% to $5.41. This appears to have been driven by a positive reaction to the retailer's half year results from brokers. One of those was Macquarie, which has responded to the results by retaining its outperform rating and lifting its price target to $5.50. Elsewhere, the team at Citi has retained its buy rating on Harvey Norman's shares with an improved price target of $5.80.

Pro Medicus Limited (ASX: PME)

The Pro Medicus share price is up 4.5% to $264.93. Investors have been buying the health imaging technology company's shares following the announcement of another big contract win. Pro Medicus has signed a $40 million, seven-year contract with LucidHealth. It is a leading provider of radiology services in the US. The company's CEO, Dr Sam Hupert, said: "LucidHealth joins our rapidly growing list of private practice clients. Their needs, which include subspecialized onsite and remote reading/ teleradiology capabilities, are uniquely catered for by our proprietary server-side streaming technology reinforcing our view that Visage 7 is ideally positioned to address this market and the other key market segments we service, which include academic medical centers, IDNs and outpatient clinics."

Synlait Milk Ltd (ASX: SM1)

The Synlait Milk share price is up 5% to 81.5 cents. This morning, the dairy processor announced that it has appointed its new CEO. Synlait Milk has appointed Richard Wyeth as its new leader. The company notes that he is a "seasoned, tested, and highly regarded CEO in New Zealand's dairy industry." He was previously CEO of both Westland Milk Products and Taupo-based dairy company Miraka.