Advertiser Direct revenue grew $8.0 million, or 34%, in the three months ended June 30, 2021 as compared to the three months ended June 30, 2020, driven primarily by growth of 89% in Media Transactions Measured for CTV and 100% in Media Transactions Measured for social channels. Advertiser Direct revenue grew $13.3 million, or 29%, in the six months ended June 30, 2021 as compared to the six months ended June 30, 2020, driven primarily by growth of 82% in Media Transactions Measured for CTV and 87% in Media Transactions Measured for social channels.
Advertiser Programmatic revenue grew $13.8 million, or 57%, in the three months ended June 30, 2021 as compared to the three months ended June 30, 2020, driven primarily by continued adoption of our premium-priced Authentic Brand Safety solution. Advertiser Programmatic revenue grew $23.8 million, or 50%, in the six months ended June 30, 2021 as compared to the six months ended June 30, 2020, driven primarily by continued adoption of our premium-priced Authentic Brand Safety solution.
Supply-Side revenue grew $1.8 million, or 35%, in the three months ended June 30, 2021 as compared to the three months ended June 30, 2020, primarily driven by increased uptake of our solutions from our platform and publisher customers. Supply-Side revenue grew $2.7 million, or 27%, in the six months ended June 30, 2021 as compared to the six months ended June 30, 2020, primarily driven by increased uptake of our solutions from our platform and publisher customers.
Cost of Revenue (exclusive of depreciation and amortization shown below)
Cost of revenue increased by $4.6 million, or 61%, from $7.7 million in the three months ended June 30, 2020 to $12.3 million in the three months ended June 30, 2021. The increase was primarily due to higher partner costs from revenue-sharing arrangements with our Advertiser Programmatic partners, as well as higher software and other technology costs to support our increased volumes. Cost of revenue increased by $7.5 million, or 50%, from $15.0 million in the six months ended June 30, 2020 to $22.5 million in the six months ended June 30, 2021. The increase was primarily due to higher partner costs from revenue-sharing arrangements with our Advertiser Programmatic partners, as well as higher software and other technology costs to support our increased volumes.
Product Development Expenses
Product development expenses increased by $4.2 million, or 39%, from $10.9 million in the three months ended June 30, 2020 to $15.1 million in the three months ended June 30, 2021. The increase was primarily due to an increase in personnel costs of $3.4 million, which reflects our continued hiring of resources to support our product-development efforts. Product development expenses increased by $8.1 million, or 38%, from $21.2 million in the six months ended June 30, 2020 to $29.3 million in the six months ended June 30, 2021. The increase was primarily due to an increase in personnel costs of $6.9 million, which reflects our continued hiring of resources to support our product-development efforts, in addition to $0.4 million of higher professional fees and $0.4 million of higher software expenses.
Sales, Marketing and Customer Support Expenses
Sales, marketing and customer support expenses increased by $6.8 million, or 53%, from $12.8 million in the three months ended June 30, 2020 to $19.6 million in the three months ended June 30, 2021. The increase was primarily due to an increase in personnel costs of $5.2 million to support our sales efforts, grow market presence in international markets, drive continued expansion with our existing customers, and support existing and new customers in addition to $1.5 million of higher stock-based compensation expense. Stock-based compensation expense increased due to certain awards that accelerated upon the completion of the IPO, an increase in the number of employees who were eligible and received equity awards and an increase in the value of our common stock. Sales, marketing and customer support expenses increased by $9.9 million, or 40%, from $25.2 million in the six months ended June 30, 2020 to $35.1 million in the six months ended June 30, 2021. The increase was primarily due to an increase in personnel costs of $9.7 million to support our sales efforts, grow market presence in international markets, drive continued expansion with our existing customers, and support existing and new customers.