Saudi Arabia, a staunch supporter of President Abdel Fattah al-Sisi's regime, has previously offered billions of dollars in aid to Egypt since the 2013 ouster of Islamist leader Mohamed Morsi.
In December, Riyadh pledged eight billion dollars in investment and aid to Egypt over five years, but it was unclear whether the Sinai offer was part of this.
Egypt's International Cooperation Minister Sahar Nasr signed a "$1.5 billion agreement with the Saudi Development Fund for developing projects in the Sinai Peninsula", a ministry statement said.
The funds will be used "for development projects" in agriculture and to build 26 residential complexes that would also include hospitals and schools.
The peninsula's northern part is a bastion of the Egyptian affiliate of the jihadist Islamic State group, which has carried out deadly attacks on Egyptian security forces since Morsi's ouster.
On Saturday, 15 policemen were killed in an attack on a police checkpoint in the area. The attack was claimed by IS.
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On Sunday, Saudi Arabia also signed a separate five-year agreement to help Egypt finance its petrol needs, the ministry said.
The fuel agreement comes despite a sharp fall in Saudi Arabia's own oil earnings amid the global decline in crude prices.
Sunday's agreements come ahead of an official visit by Saudi King Salman to Cairo on April 4.
Ties between Cairo and Riyadh have strengthened since then army chief Sisi ousted Morsi in July 2013, with Egypt joining a Saudi-led coalition that has battled Iran-backed rebels in Yemen since March last year.
Egypt's Gulf allies Saudi Arabia, Kuwait and the United Arab Emirates each offered $4 billion in investment and aid to Cairo in March 2015.
Cairo, fighting the deadly IS-led insurgency in North Sinai, has been criticised by rights groups for its blistering crackdown on Morsi's Muslim Brotherhood since 2013.
The police crackdown has left hundreds of people dead and thousands imprisoned.
Egypt, Saudi Arabia and the UAE have all declared the Muslim Brotherhood to be a "terrorist group".